EDP Sciences
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Volume 376, Number 3, September IV 2001
Page(s) 878 - 884
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20011045

A&A 376, 878-884 (2001)
DOI: 10.1051/0004-6361:20011045

HST NICMOS photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4

S. Ortolani1, B. Barbuy2, E. Bica3, A. Renzini4, M. Zoccali4, R. M. Rich5 and S. Cassisi6

1  Università di Padova, Dept. di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: ortolani@pd.astro.it
2  Universidade de São Paulo, CP 3386, São Paulo 01060-970, Brazil
    e-mail: barbuy@iagusp.usp.br
3  Universidade Federal do Rio Grande do Sul, Dept. de Astronomia, CP 15051, Porto Alegre 91501-970, Brazil
    e-mail: bica@if.ufrgs.br
4  European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching bei München, Germany
    e-mail: arenzini@eso.org
5  Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562, USA
    e-mail: rmr@astro.ucla.edu
6  Osservatorio Astronomico Collurania, 64100 Teramo, Italy
    e-mail: cassisi@astrte.te.astro.it

(Received 5 June 2001 / Accepted 16 July 2001 )

We present results from NICMOS Hubble Space Telescope observations of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4, obtained through the filters F110W (1.1 $\mu$m) and F160W (1.6 $\mu$m) (nearly equivalent to J and H). For the first time the turnoff region of Liller 1 and the main sequence of Terzan 5 and Terzan 4 are reached, as well as the horizontal branch of UKS 1. The magnitude difference between the turnoff and the red horizontal branch $\Delta m_{110}=m_{110}^{\rm HB}- m_{110}^{\rm TO}$ is used as an age indicator. From comparisons with new isochrones in the NICMOS photometric system, we conclude that the two metal-rich clusters NGC 6528 and Terzan 5 are coeval within uncertainties (~$20\%$) with 47 Tucanae. Liller 1 and UKS 1 are confirmed as metal-rich globular clusters. Terzan 4 is confirmed as an interesting case of a metal-poor cluster in the bulge with a blue horizontal branch.

Key words: Galaxy: globular clusters: individual: NGC 6528, Terzan 5, Liller 1, Terzan 4 UKS 1 -- stars: CM diagram

Offprint request: M. Zoccali, mzoccali@eso.org

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